In general, a mobile communication system has been developed for the purpose of providing communications while securing user's mobility. With the rapid progress of technology, such a mobile communication system can now provide not only voice communications but also high-speed data communication services.
Recently, as one of the next-generation of mobile communication systems, standardization of a Long Term Evolution (LTE) system in the 3rd Generation Partnership Project (3GPP) is currently underway. The LTE system is a technology to implement high-speed packet-based communication having a transmission speed of about 100 Mbps at maximum, which is higher than the data transmission speed that is currently provided, and the standardization thereof has already been completed at present.
Current, discussion of a Long Term Evolution-Advanced (LTE-A) system has been regularized, which improves the transmission speed through grafting of various new technologies on the LTE communication system. A representative one of the newly introduced technologies may be carrier aggregation. The carrier aggregation corresponds to a case where one terminal uses a plurality of forward carriers and a plurality of reverse carriers, unlike a case where a terminal performs data transmission/reception using one forward carrier and one reverse carrier as in the related art.
Currently, in the LTE-A, only intra-ENB carrier aggregation has been defined. This may result in the reduction of applicability of the carrier aggregation function, and particularly, in a scenario in which a plurality of pico cells and one macro cell operate to overlap each other, this may cause problems in that the macro cell and the pico cells are unable to be aggregated.